Case hardening method



ifaicentd Jan. 13, 193i uuireosrarss fm'1 r'r.1-rr orrics PORTER w. SHIMER AND EDWARD B. SHIMER, or ms'ron, PENNSYLVANIA, ASSIGNORS 'ro AMERICAN CYANAMID comrm, on NEW YORK, N. Y., A CORPORATION or MAINE CASE HARDENING METHOD No Drawing. Original application filed February 23,: 1929, Serial No. 342,290. Divided and this application filed January 16, 1930. Serial No. 421,259.

This invention relates to methods ofcase hardening metals, and is a division of our co-pending application Serial No. 342,290 filed February 23, 1929.

One method of case hardening metals that has heretofore been used to a considerable extent is the immersion of the metal parts ing gases from the bath and are very poisonous.

In Patents Nos. 1,279,457 and 1,279,458

-both granted on September 17th, 1918 to Porter W. Shimer, one ofthe present applicants, there is described a molten bath consisting of mixtures of calcium chloride, barium chloride and sodium chloride, potassium chloride and sodium chloride and other similar compounds and mixtures. Such a molten bath is caused to acquire case hardening properties by immersing calcium cyanamid therein. The process of the Shimer patents is particu larly advantageous as the cyanamid is not poisonous, is readily obtainable at a moderate cost and does not emit irritating and danger- ,ous gases when immersed in a bath of molten salts. The gases evolved in the bath burn at the surface and are non-poisonous and nonirritating.

When a case hardening bath of the character described in the Shimer patents is used for a longtime, especially under crude operating conditions, it gradually loses its power of acquiring full case hardening properties by the immersion of additional calcium cyanamid therein. This loss of power to acquire full case hardening properties is sometimes augmented by a long continued use of the bath on large production scale, particularly when the articles being case hardened are coated with scale or when cast iron pots are used to contain the bath. This deterioration of the bath is accompanied by the formation of a film of inert and relatively impenetrable material over the surface of the calcium cyana'mi'd which prevents reaction of the calcium cyanamid with the bath and thus lessens its effectiveness to impart case hardening properties to the bath. Even the addition of fresh cyanmid to the bath does not produce the desired reactivation since the fresh cyanamid also becomes coated with this inert and substantially impenetrable film.

In patents Nos. 1,518,607 and 1,532,663

issued December 9th. 1924 and April 7th,

1925, respectively, to Porter W. Shimer, one of thepresent applicants, there is described several methods of reactivating such deteriorated baths of fused salts. These methods consist in adding to the bath a reducing agent, such as aluminum, or other active reagent such as SOdlllIIl cyamde; When the reducing agent is added to the bath, a noticeable activity is obtained therein followed by the separation of dross which may be re- .moved from the bath by means of a perforated ladle. The removal of these impurities fully restores the case hardening properties of the bath and such purification or renewal of the bath may be resorted to when necessary.

In the present invention we provide a case hardening process in which the case hardening strength of the bath may be maintained more uniform and in which the separation of dross is brought about by the addition of the case hardening agent. Instead of renewing the case hardening strength of the bath at infrequent intervals by the addition of a relatively large quantity of calcium cyanamid,'we add. a case hardening'compound to the bath at regular and frequent intervals so that the case hardening strength of the bath is maintained more or less constant and .the impurities that would otherwise collect in the bath may be removed therefrom at the time of each addition of the case hardening compound. Instead of obtaining a slow accumulation of objectionable residues the bath is kept clear and caused to retain its case hardening properties by the regular, direct and more or less frequent addition of case hardening material.

Various materials may be employed for imparting case hardening properties to a bath by our new process. We have found, howsubstances which we term cyanamid cyanides are employed. Such a cyanide may be formed by fusing calcium cyanamid with sodium chloride. In the Erlwein and Frank Patent No. 798,333, issued September 2nd, 1902, there is described the manufacture of calcium cyanide by fusingcalcium cyanamid and carbon in the presence of a sodium chloride flux. Crude calcium cyanamid, however, contains suflicient carbon as an impurity to unite with the CN radical of the cyanamid and produce the CN radical of the cyanide. As set forth in the Erlwein and Frank patent, page 1, line 95 to page 2, line 6, and in an. article by Dr. W. S. Landis entitled A new cyanide appearing on page 265, Volume XX I, No. 6, of Chemical and Metallurgical Engineering (Feb. 11, 1920) a crude calcium cyanide can be obtained from crude calcium cyanamid by fusing the calcium cyanamid with sodium chloride with-- out the addition of carbon. This crude calcium cyanide, which. we term cyanamid cyanide, contains sodium chloride, carbon, free 'lime and calcium cyanamid as impurities. The cyanamid cyanide or crude calcium cyanide, may be added to a bath of fused salts regularly and periodically in minute proportions, such as percent of the weight of the bath orounce to a, 15 pound bath. A bath of the type disclosed in the prior patents of Porter W. Shimer may be 'em-' ployed, but we preferably employ a bath. obtained by fusing dry sodium chloride and dry. calcium chloride in proper proportions. While we have obtained ood case hardening with the addition of as ttle as of 1 ercent of cyanamid cyanide, or crude calcium cyanide, to the weight of the melt, we do not wish to limit ourselves to this amount and contemplate, when desirable, using additions up to 1 percent of the weight of the melt. The-exact amount and frequency of these additions naturally varies according to the circumstances, such as the size of the bath, the shape of the pot, the temperaturethe amount of work or articles to be case hardened, the quantity of the bath materials removed by adherence to the articles and the like. We have found that in a number of cases the regular hourly additions of percent by weight of cyanamid cyanide, or crude calcium" cyanide, to the bath serve to keep the strength of the bath constant through the day with consequent uniformity of depth and hardness of case.

In accordance with the present invent-ion we have'found that the regular and more or less frequent addition to a bath of fused salts of comparatively small amounts of crude calcium cyanide has produced excellent case hardening results. This regular addition of small amounts of the case hardening material maintains the case hardening properties of the bath substantially constant with a consequent procurement of a uniform-depth and hardness of case on the articles immersed therein. The direct addition of a cyanide to the bath, instead of the formation of a" cyanide within the bath, as occurs when .a cyanamid added, produces excellent case hardening results.

Instead of using calcium'cyanamid. and

sodium chloride in the manufacture of cyanamid cyanide and obtaining a crude calcium cyanide other cyanamid cyanideshmay be formed by fusing other alkaline earth cyanbath has the effect of considerably prolonging the life of the cyanamid previously immersed therein, [The cyanamid at the bottom of themelt acts as a-back log and gives ofi' case hardening activity throughout the. run, while the addition of the small amount of cyanamid cyanide equalizes the activity of the bath and enables the user to obtain a much longer life from the cyanamid. In this waythe effectiveness of the cyanamid is doubled and often trebled. a It will be seen that our new process of case hardening metals hasmany advantages over former methods. Harder, deeper and more uniform cases may be obtained with greater economy and-ease of operation. The. casehardening bath retains its case hardening properties more uniformly when case hardening properties are imparted to the bath by' regular and more or less frequent additions of crude calcium cyanide. As stated above, the bath may consist of a mixture of dry fused salts towl ich the case hardening properties are imparted by these small but regular additions of-crude calcium cyanide, or the bath may originally contain a case hardening material, suchas calcium cyanamid, the actlvity of which is extended and increased by'theso f small additions of crude calcium cyanide.

We claim: I

1. The method of imparting to and main taining case hardening propert1es.1n a'moltcn bath of fused salts, which consistsjin regularly addingat frequent intervals relatively small amounts of a cyanide of the alkali earth metals.

2. The method of imparting to and maintaining case hardening properties in a molten bath made by fusing a mixture of dry calcium chloride and dry'sodium chloride, which consists in introducing at frequent mtervals relatively small amounts of cyanide of an alkali earth metal.

3. The method of increasing and prolonging the case hardening properties of a molten bath of fused salts containing a cyanamid, which consists in regularly adding at frequent intervals relatively small amounts of an alkali earth cyanide.

4. The method of increasing and prolonging the case hardening properties of a molten bath of fused salts containing a cyanamid, which consists in regularly adding, at frequent intervals, relatively small amounts of a metallic cyanide.

5. The method of increasing and prolonging the case hardening properties of a. molten bath of fused salts containing a cyanamid, which consists in regularly adding, at frequent intervals, relatively small amounts of.

calcium cyanide.

6. The method of increasing and prolonging the case hardening properties of a molten bath of fused chlorides containing a cyanamid, which consists in regularly introducing at frequent intervals relatively small amounts of a cyanide. V

In testimony whereof we aifix our signatures.

PORTER W. SHIMER. EDW. B. .SHIMER. 

